The two black holes, with masses of 32 and 19 masses of the Sun, collided and merged into a single black hole of 49 Solar masses. (The difference in the final mass is the result of dissipation of energy as gravitational waves.) The collision happened about 3 billion light years away. This is farther than LIGO's first or 2nd detection, which happened 1.3 and 1.4 billion light years away, respectively.

The discovery took place on January 4, 2017 during LIGO's Second Observing Run. It reaffirms the existence of black holes that are heavier than 20 Solar masses, the fact that was unknown before the LIGO discoveries. Earlier studies, made with X-ray observations, predicted black holes with masses up to 20 Solar masses. The three LIGO discoveries confirm the existence of black holes with masses larger than 20 Solar masses.

Image: LIGO has discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). The three confirmed detections by LIGO (GW150914, GW151226, GW170104), and one lower-confidence detection (LVT151012), point to a population of stellar-mass binary black holes that, once merged, are larger than 20 solar masses—larger than what was known before. Image credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

LIGO Laboratory is the U.S. national facility for gravitational-wave research. The first detections of gravitational waves by LIGO in 2015 haveopened the field of gravitational-wave physics and astronomy. Funded by the National Science Foundation, LIGO Laboratory's mission is to observe gravitational-wave sources, to operate the LIGO Hanford and Livingston Observatories in support of national and international scientific community,to carry out research and development for future gravitational-wave detectors, and to carry out scientific education and public outreach related to gravitational wave astronomy.